1. Field of the Invention
The present invention relates to an indium-zinc-oxide semiconductor ink composition in which a spontaneous combustion reaction occurs, and an inorganic semiconductor thin film produced thereby.
2. Description of the Related Art
As recent interest on characteristics of oxide semiconductors including diversity grows, studies have been actively undergoing. In particular, the oxide semiconductor has been applied as an active layer for the thin film transistor (TFT). The inorganic oxide semiconductor used for the above is exemplified by zinc oxide (ZnO), indium oxide (IZO), indium-zinc-oxide (IZO), indium-gallium-zinc-oxide (IGZO), and indium-zinc-tin-oxide (IZTO), etc. According to the chemical bond of the oxide, the oxide semiconductor has a comparatively big band gap of at least 3 eV, which is transparent in visible ray, is advantageous for low temperature processing, compared with silicone, and facilitates solution process with less costs and high mobility as well.
The thin film transistor element is a key part of display information appliance. That is, the element is essential for gradation of display information appliance by playing a role in switching a pixel. Therefore, the market of such thin film transistor element is growing quite big in electronic & information industry. Recent methods to prepare the oxide semiconductor are exemplified by sputtering, atomic layer deposition (ALD), pulsed laser deposition (PLD), and metal organic chemical vapor deposition (MOCVD), etc.
As the price of electronic parts of display device gets lower, the interest on electronic & information industry has been focused on the super-low-cost, large area process, and mass-production. To replace the photolithography or vacuum deposition which requires high costs, it is necessary to develop a solution based process. To prepare the thin film transistor element based on the solution process, organic semiconductors have been a target of study. However, the organic thin film transistor still has problems to be improved, which includes the basic properties of a thin film transistor such as mobility, on/off ratio, and current density, etc, and further durability and electrical reliability.
Recently there is a new attempt to produce an inorganic oxide semiconductor using a solution process. Accordingly, studies to develop a low temperature process with various materials such as indium oxide, indium-tin-oxide, aluminum and gallium added zinc oxide film, etc, have been actively going on. The solution process is exemplified by sol-gel process, metal organic decomposition (MOD), and chemical bath deposition (CBD), etc.
The sol-gel process that has been used for the production of an inorganic oxide semiconductor is characterized by spin coating using a metal precursor solution at a proper pH or ink-jet printing on a substrate, both of which require heat-treatment thereafter. During the heat-treatment, the inorganic precursor is hydrolyzed and condensated, from which a metal oxide is generated by conjugating metal and oxygen. The said inorganic precursor is exemplified by metal alkoxide, metal acetate, metal nitrate, and metal halide, etc.
The temperature for the sol-gel oxide semiconductor process is still a little too high to secure the excellent electronic characteristics. According to the previous reports, the temperature for heat treatment of ZnO, IZO, and IGZO are respectively at least 300° C., 400° C., and 450° C. (Adv. Mater. 2012, 24, 2945).
Various attempts have been made to overcome the disadvantage in the heat-treatment process of the inorganic semiconductor material. According to Shrringhaus et al., indium, gallium, and zinc alkoxide precursors were heat-treated at 275° C. in a glove box in nitrogen atmosphere to obtain the mobility of ˜10 cm2V−1s−1. According to Park et al., indium, gallium, zinc acetate, and nitrate precursors were exposed with deep-UV and heat-treated at 200° C. in a box in nitrogen atmosphere, and as a result the mobility of ˜10 cm2V−1s−1 on the aluminum oxide insulator substrate was obtained (Nature 2011, 10, 45., Nature Lett. 2012, 489, 128).
However, the above methods can only be accomplished in nitrogen atmosphere with a special device or a high-K gate insulator, indicating that the methods are not practical and have poor industrial usability thereby.
According to the study of Marks et al., a metal precursor composition that is suitable for combustion reaction was prepared by adding the fuel material Urea and the oxidizer material NH4NO3 to indium and zinc nitrate precursors. After treating the composition with high heat at 300° C., the mobility of ˜3 cm2V−1s−1 was obtained. Even though high mobility was obtained at a comparatively low temperature by using combustion reaction, the fuel material, the oxidizer material, and the base solution had to be added in addition to the metal oxide precursor. That is, the said method cannot be achieved without the quantitative addition of such materials (J. Am. Chem. Soc. 2012, 134, 9593, Nature Mater. 2011, 10, 382, J. Am. Chem. Soc. 2012, 134, 11583).
In the course of study to prepare an indium-zinc-oxide semiconductor thin film having excellent properties, the present inventors identified metal precursors in which the fuel material and the oxidizer material are coordinated. By mixing these two precursors without any additional materials, the inventors could develop an inorganic semiconductor ink composition usable for the preparation of an indium-zinc-oxide semiconductor thin film with improved charge carrier mobility and on/off ratio, leading to the completion of this invention.